Britain’s competition watchdog said on Wednesday that Paypal Holdings’s $2.2 billion takeover of Swedish financial technology startup iZettle would be referred for an in-depth review.

The Competition and Markets Authority (CMA) said Paypal had refused to offer proposals to address its concerns on how the deal, Paypal’s biggest ever, could hurt competition and could lead to higher prices for customers, or worse quality of service.

The regulator had also flagged concerns surrounding competition in the emerging market for “omni-channel” payment services as a result of the merger.

Paypal’s acquisition of iZettle, which would allow the US payments processor to expand into the retail payment terminals business in international markets, closed in September.

The deadline for a final decision on the matter is May 21, 2019, the CMA said.

Paypal was not immediately available for a comment. US markets are closed to mark former President George HW Bush’s death.

Founded in 2010, iZettle is one of the largest fintech startups to emerge from Europe, and one of a string of successful venture-backed companies to emerge from Sweden in the past decade or more.